Technical Abstract:
Haemonchus contortus is one of the principal stomach worms of sheep, and infection is characterized by anemia. Estimates of the average blood loss per worm per day range from .003 to .05 ml. Studies have shown that high eosinophilia was correlated with low fecal egg count (FEC) and, therefore, resistance for the infected sheep. Others have measured the association between FEC and hematocrit. The purpose of this study was to estimate correlations between FEC in pasture-raised lambs and blood parameters measured on an automated hematology analyzer. We collected blood and fecal samples from 108 cross-bred lambs one week after weaning and removal from contaminated pastures (84.1 d ± 6.2, 43.8 lb ± 8.43). Lambs were not dewormed until after samples were collected. FEC were determined by the McMaster method, and blood was analyzed using a HemaVet® Mascot multispecies hematology system. Eosinophil (EO) numbers ranged from 0 to 0.42 K/µl, EO% ranged from 0 to 4.66. Red blood cell (RBC) numbers ranged from 4.13 to 14.00 M/µl, hemoglobin (HB) ranged from 4.2 to 12.1 g/dL, hematocrit (HCT) ranged from 11.2 to 33.3%, mean corpuscular volume ranged from 22.6 to 32.6 fL, and eggs per gram (EPG) ranged from 0 to 19,200. Data were analyzed using the GLM procedure multivariate analysis of variance in SAS. The correlation coefficients of EPG with either EO measurement were low; however, the associations between RBC, HB, and HCT with EPG were -0.48, -0.48, and -0.47, respectively. Our results indicate that RBC values are more informative than EO measurements in determining the effect of H. contortus infection on lambs. To minimize pasture contamination, replacement animals with low EPG and high RBC, HB, and HCT values should be selected.